Point-to-point links: Install an SEL-3021 at each end of the link, for SCADA, I&C, ATM, and more

Multidrop Master/Remote Links: Install an SEL-3021 at the master and each remote link of a multidrop network.

Maintenance Ports with Multiple Maintenance Technicians: Install an SEL-3021 on each maintenance port or port switch. Provide each authorized engineer or technician with an SEL-3021, set to match the encryption settings of the maintenance ports.